1. Field of the Invention
The present invention relates to straight-chain organopolysiloxanes having fluorine-containing organic groups useful as a silicone oil of which various applications are known and also useful as a raw material for rubberlike cured products.
2. Description of Prior Art
Since straight-chain organopolysiloxanes having fluorine-containing organic groups are low in surface tension and refractive index and excellent, for example, in electric insulating properties, reliability, water repellency, anti-foamability, oil resistance, solvent resistance, lubricity, and heat resistance, they are used in various applications in wide industrial fields.
Conventionally, as those straight-chain organopolysiloxanes having fluorine-containing organic groups, many straight-chain organopolysiloxanes having 3,3,3-trifluoropropyl groups are known and as straight-chain organopolysiloxanes having longer fluorine-containing organic groups, for example, straight-chain organopolysiloxanes having long-chain fluoroalkyl ether groups represented by the following general formula (7): EQU F--(C.sub.b F.sub.2b O).sub.c --C.sub.d F.sub.2d --CH.sub.2 OR.sup.4 --(7)
wherein b is an integer of 1 to 3, c is an integer of 1 to 5, d is 1 or 2, and R.sup.4 represents a bivalent organic group having 3 to 10 carbon atoms and free from fluorine are known (U.S. Pat. No. 5,118,775 corresponding to Japanese Preexamination Patent Publication (KOKAI) No. 2-219829 and U.S. Pat. No. 5,116,928 corresponding to Japanese Preexamination Patent Publication (KOKAI) No. 2-219830).
As methods of producing straight-chain organopolysiloxanes having fluorine-containing organic groups, methods wherein a cyclotrisiloxane having such a fluorine-containing organic group alone or optionally in combination with a cyclotrisiloxane containing no fluorine, such as hexamethylcyclotrisiloxane, is subjected to ring opening polymerization in the presence of a catalyst, such as sulfuric acid, activated clay, acid-treated activated clay, a hydroxide or a silanolate of an alkali metal, a quaternary ammonium hydroxide, and a quaternary phosphonium hydroxide are known (U.S. Pat. No. 3,483,270 corresponding to Japanese Patent Publication (KOKOKU) No. 46-27267; E. E. Bostick, ACS Polymer Preprint 10 (2), 877 (1969); and Japanese Pre-examination Patent Publication (KOKAI) No. 1-294738).
However, if it is tried to obtain a straight-chain organopolysiloxane having fluorine-containing organic groups by the above production method, in addition to the intended straight-chain organopolysiloxane, cyclic siloxanes and low-molecular-weight straight-chain siloxanes are produced concomitantly, and particularly cyclic siloxanes having three to several tens of repeat units are produced. Of these, low-molecular-weight straight-chain siloxanes and cyclic siloxanes having a low degree of polymerization can be removed by heating the obtained polymer under reduced pressure, but the removal of cyclic siloxanes having a molecular weigher of about 800 or over, particularly cyclic siloxanes having a molecular weight of about 1,500 or over, is very difficult. Therefore, where the thus obtained straight-chain organopolysiloxane having fluorine-containing organic groups is used as an oil or as a raw material or additive for rubberlike cured products, coatings, etc. by known techniques, the remaining cyclic siloxanes evaporate gradually from the rubberlike cured product or bleeding occurs on the surface of the rubberlike cured product, which causes electrical contact trouble in the field of electricity and environmental contamination or the like in the field of building materials. Cyclic siloxanes that cause such trouble and problems are generally cyclic siloxanes having a molecular weight of 3,000 or below.
Therefore, it is desired to develop straight-chain organopolysiloxanes having fluorine-containing organic groups that are substantially free from low-molecular-weight straight-chain siloxanes and cyclic siloxanes having a low degree of polymerization as well as cyclic siloxanes having a molecular weight of 3,000 or below.